1. Field of the Invention
The present invention relates generally to call processing in a media gateway and, more particularly, to a method of controlling common call connection and a media gateway for executing the method, which are capable of performing call connection control without a change in a control procedure under different protocols and the interworking of the different protocols.
2. Description of the Related Art
A media gateway is a device for converting the type of a traffic format according to a communication network. The media gateway functions to convert the Time Division Multiplexing (TDM) traffic of a circuit network into the Asymmetric Transfer Mode (ATM) or Internet Protocol (IP) traffic of a packet network chiefly in a next-generation packet voice transmission network. The media gateway is allowed to interwork with a softswitch by a control protocol (for example, Media Gateway Control Protocol (MGCP), Megaco, etc.) and determines traffic flow paths to control calls. The transmission of information between a plurality of media gateways is performed using Real-time Transport Protocol (RTP) in the case of IP, or using Permanent Virtual Connection (PVC) or Switched Virtual Connection (SVC) in the case of ATM.
For the control protocols of a Media Gateway, there exist a Megaco/H.248 of International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) and Internet Engineering Task Force (IETF) and MGCP of IETF. For a signaling protocol that can be installed when such a media gateway is used as a gateway, there exist Session Initiation Protocol (SIP) of IETF and H.323 of ITU-T. These protocols are installed in the media gateway, and function to control sources, such as a TDM channel and a RTP channel, the attributes of channels and call connection.
MGCP is a set of rules that governs how information is to be exchanged between a Media Gateway Controller (MGC) and a media gateway. As an MGC and a media gateway were separated from each other by dividing the function of a conventional media gateway in which a signaling plane and a control plane existed in the same system, MGCP was proposed to cope with the separation. MGCP has the functional characteristics of supporting the implementation of various services in the media gateway controller. MGCP is currently used widely on Voice over Internet Protocol (VoIP), and has defects in scalability and multimedia service support.
For the new control protocol of a media gateway having functions, such as scalability, to overcome the defects of the MGCP and support various VoIP services, there exists Megaco/H.248. For technology for supporting multimedia services under a Local Area Network (LAN) that does not guarantee Quality of Service (QoS), there exist H.323, which is currently used widely on IP networks to support telephony services. However, H.323 has disadvantages in simplicity and scalability, so that the advantages of SIP are highlighted. Currently, many companies have developed SIP and have applied and used SIP to and on IP networks. H.323 and MGCP have some disadvantages. However, H.323 and MGCP are currently used widely on IP networks to support Internet telephony services, and have advantages in view of service stability.
Since the various control protocols of a media gateway described above are being used, media gateway manufacturers must manufacture media gateways having structures capable of supporting the various protocols.
In particular, methods of controlling call processing are different from each other according to the control protocols of a media gateway, so that methods of controlling call connection in a media gateway are different from each other according to the control protocols. In the past, whenever a new protocol was installed in a media gateway, there was the inconvenience of changing a method of controlling call connection accordingly.
FIGS. 1a to 1e are views illustrating call connection control models based on various protocols. FIG. 1a is view showing a call connection model based on MCGP, which includes ‘call’ corresponding to a call, and ‘endpoint’ and ‘connection’ corresponding to channels that are connected to each other in the call. FIG. 1b is a view showing a call connection control model based on H.323 signal protocol, which includes ‘call’ corresponding to a call and ‘channel’ corresponding to a channel. FIG. 1c is a view showing a call connection control model, which includes ‘context’ corresponding to a call and ‘termination’ corresponding to a channel.
When call connection is performed between different services, call connection may be controlled by the interworking of different protocols. FIG. 1d is a view showing the interworking of H.323 and SIP. FIG. 1e is a view showing the interworking of H.323 and Megaco.
It can be appreciated from the above that call connection models are different from each other according to the protocols. Accordingly, inconvenience arises in that, whenever a new protocol is applied to a media gateway, a method of controlling call connection must be changed.
Since call connection control Application Program Interfaces (APIs) provided to control a media gateway are different from each other according to manufacturers, it has been further necessary to implement the porting of call connection control APIs according to protocols.
For reference, there has been proposed a VoIP gateway using SIP that can reduce control time by controlling media processing using SIP that is a specific type of call control protocol (Myeonggun LEE, “VoIP gateway design and implementation based on SIP,” Proceedings (second volume) of Spring academic thesis conference of Korea Information Processing Society, Vol. 9, No. 1, Apr. 13, 2002).
The thesis discloses a method of controlling call based on a specific call control protocol, and does not solve the problems of the preceding technologies.